(function(win, lib) {

  var doc = win.document;

  var docEl = doc.documentElement;

  var metaEl = doc.querySelector('meta[name="viewport"]');

  var flexibleEl = doc.querySelector('meta[name="flexible"]');

  var dpr = 0;

  var scale = 0;

  var tid;

  var flexible = lib.flexible || (lib.flexible = {});



  if (metaEl) {

//console.warn('将根据已有的meta标签来设置缩放比例');

    var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/);

    if (match) {

      scale = parseFloat(match[1]);

      dpr = parseInt(1 / scale);

    }

  } else if (flexibleEl) {

    var content = flexibleEl.getAttribute('content');

    if (content) {

      var initialDpr = content.match(/initial\-dpr=([\d\.]+)/);

      var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/);

      if (initialDpr) {

        dpr = parseFloat(initialDpr[1]);

        scale = parseFloat((1 / dpr).toFixed(2));

      }

      if (maximumDpr) {

        dpr = parseFloat(maximumDpr[1]);

        scale = parseFloat((1 / dpr).toFixed(2));

      }

    }

  }



  if (!dpr && !scale) {

    var isAndroid = win.navigator.appVersion.match(/android/gi);

    var isIPhone = win.navigator.appVersion.match(/iphone/gi);

    var devicePixelRatio = win.devicePixelRatio;

    if (isIPhone) {

// iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案

      if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {

        dpr = 3;

      } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)){

        dpr = 2;

      } else {

        dpr = 1;

      }

    } else {

// 其他设备下，仍旧使用1倍的方案

      dpr = 1;

    }

    scale = 1 / dpr;

  }



  docEl.setAttribute('data-dpr', dpr);

  if (!metaEl) {

    metaEl = doc.createElement('meta');

    metaEl.setAttribute('name', 'viewport');

    metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');

    if (docEl.firstElementChild) {

      docEl.firstElementChild.appendChild(metaEl);

    } else {

      var wrap = doc.createElement('p');

      wrap.appendChild(metaEl);

      doc.write(wrap.innerHTML);

    }

  }



  function refreshRem(){

    var width = docEl.getBoundingClientRect().width;

    if (width / dpr > 540) {

      width = 540 * dpr;

    }

    var rem = width / 10;

    docEl.style.fontSize = rem + 'px';

    flexible.rem = win.rem = rem;

  }



  win.addEventListener('resize', function() {

    clearTimeout(tid);

    tid = setTimeout(refreshRem, 300);

  }, false);

  win.addEventListener('pageshow', function(e) {

    if (e.persisted) {

      clearTimeout(tid);

      tid = setTimeout(refreshRem, 300);

    }

  }, false);



  if (doc.readyState === 'complete') {

    doc.body.style.fontSize = 12 * dpr + 'px';

  } else {

    doc.addEventListener('DOMContentLoaded', function(e) {

      doc.body.style.fontSize = 12 * dpr + 'px';

    }, false);

  }





  refreshRem();



  flexible.dpr = win.dpr = dpr;

  flexible.refreshRem = refreshRem;

  flexible.rem2px = function(d) {

    var val = parseFloat(d) * this.rem;

    if (typeof d === 'string' && d.match(/rem$/)) {

      val += 'px';

    }

    return val;

  }

  flexible.px2rem = function(d) {

    var val = parseFloat(d) / this.rem;

    if (typeof d === 'string' && d.match(/px$/)) {

      val += 'rem';

    }

    return val;

  }



})(window, window['lib'] || (window['lib'] = {}));
